Increase in the capacity and the speed of information treated by signal reader, particularly by digital disk driver, is remarkable in recent years. Thus the recording information density has become larger than ever owing to the increase in the speed multiplication of CD-ROM disk and to the popularization of DVD.
The disk of the digital disk drive r generates vibration caused by eccentricity, face deflection, rotational vibration, and the like. Accordingly, on reading information from a disk, if laser is applied, the focal point of laser and the position of information to be read give an offset to each other, which raises a reading error.
To prevent the reading error, conventional signal readers adopt a mechanism to correct the offset caused by vibration and the like. Nevertheless, owing to the above-described increase in the vibration resulted from the increased vibration caused by the recent increase in the speed of digital disk driver and to the increase in the vibration frequency and the information density, the requirement for improving the vibration damping property and for increasing the resonance frequency in the signal reader has become severer than ever.
Under the above-described circumstance, the conventional thermoplastic resin materials for existing signal readers cannot achieve stable reading performance. Furthermore, the components of signal reader and other structural parts are requested to perform quick response to satisfy the increased speed multiplication. The response largely depends on the weight of the signal reader and other structural parts. As a result, a material having small specific gravity is wanted.
According to the related art, the request for small specific gravity of the material was answered by reducing the amount of filler and by combined use of hollow inorganic filler.
Along with the increased speed multiplication, however, the heat generation on the digital disk driver has become a problem of failing in attaining the stable signal reading accuracy. The problem raises a request for high heat dissipation material.
JP-A 2001-172479 discloses a liquid crystalline polyester resin composition having light weight and low thermal conductivity, which resin is composed of 100 parts by weight of LCP, 2 to 50 parts by weight of a hollow sphere having 5 to 500 μm of average particle size and 60 to 80% of hollow percentage, and 0 to 40 parts by weight of an inorganic fiber, while giving 10 to 50 of X designating the break rate of the hollow sphere (refer to claims 1 to 4, Examples and Table 1 of JP-A 2001-172479).
The disclosed technology, however, does not describe or suggest that the material can be used as an adequate one for increasing the resonance frequency and for improving the vibration damping property in the signal reader. The Example in the disclosure describes that the thermal conductivity is 0.42 W/m·K or smaller and that higher than the range is not suitable.
JP-A 2004-27021 discloses a molding article prepared by injection molding of a composition composed of 90 to 45% by weight of an wholly-aromatic liquid crystalline polyester having 320° C. or higher melting point, 10 to 40% by weight of an inorganic hollow sphere having 2 or smaller aspect ratio, and 0 to 15% by weight of an inorganic filler having 4 or larger aspect ratio. The molding article is an wholly-aromatic liquid crystalline polyester resin composition giving 3.0 or smaller dielectric constant and 0.04 or smaller dielectric dissipation factor, and shows heat resistance of resistance to solder reflow and the like, and excellent dielectric characteristics. Consequently, the molding article is used for a fixing or holding member of transmission and receiving parts of information communication devices which are used in high frequency band such as microwave and millimetric wave, (refer to claims 1 to 7 and Examples of JP-A 2004-27021).
The disclosure of the technology, however, does not describe or suggest that the molding article realizes the increase in the resonance frequency and has effective vibration damping property, and that the molding article can be used as a material for signal reader having large thermal conductivity.